Grinding cup and wear part with vibration dampening means

ABSTRACT

The present invention relates to a grinding cup and a wear part for grinding of cutting inserts of a rock drill bit. The grinding cup is provided to be rotatably mounted in a grinding machine. The grinding cup is provided to perform grinding of cutting inserts of a rock drill bit. The grinding cup comprises a shank, a flush channel, and a wear part having a recess. The grinding cup has a center axis and is provided with vibration dampening means. The wear part is resilient in the grinding cup in at least the axial direction relative to the shank and the vibration dampening means forms contact surfaces with cooperating parts. The contact surfaces have substantially the same radial extension.

TECHNICAL FIELD

The present invention relates to a grinding cup for grinding of cuttinginserts of a rock drill bit, said grinding cup comprising a shankrotatably mounted in a grinding machine and a wear part being providedwith a recess effectuating the grinding of the cutting inserts. Theinvention also relates to a wear part for the grinding cup.

PRIOR ART

During grinding of cemented carbide cutting inserts of a drill bit, agrinding cup of the above-captioned type is often used. The wear part ofsuch a grinding cup usually has an abrasive grinding surface which oftencomprises diamond particles. A grinding cup for a handheld insertgrinding machine is known through SE-B-469 970. The grinding cup isprovided with a specially designed rubber bushing, which has beenmounted to the shank of the grinding cup. The function of the bushing isto decrease the transfer of vibrations from the grinding cup to thehandheld holder body of the grinding cup. The bushing is however,mechanically unprotected, such that the bushing may be subjected tomechanical and abrasive loads.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a grinding cup thatreduces transfer of vibrations from the grinding cup to the grindingspindle in connection with grinding of drill bit cutting inserts byavoiding entrance of abrasive material to the active contact surfaces.Other objects of the present invention is to provide a grinding cup thathas a good stability and a good length of life. The above-mentionedobjects have been achieved by providing a grinding cup that ischaracterized by the features of the appended claims.

DESCRIPTION OF THE FIGURES

Below embodiments of a grinding cup according to the present inventionwill be described with reference to the appended drawings, wherein:

FIG. 1 shows a side view of a grinding cup according to the presentinvention;

FIG. 2 shows a side view of an alternative embodiment of a grinding cupaccording to the present invention;

FIG. 3 shows a side view of still another alternative embodiment of agrinding cup according to the present invention;

FIG. 4 shows still another alternative embodiment of a grinding cupaccording to the present invention, in a partly sectioned side view; and

FIG. 5 shows a cross-section of an exchangeable wear part according tothe present invention, according to the line V--V in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The grinding cup 10 according to FIG. 1 comprises a shank 11, a wearpart 12 and an intermediate portion 13 connecting the shank 11 with thewear part 12. Preferably the shank 11 and the intermediate portion 13are made in one piece. The intermediate portion consists of a number ofconnected components, see below. The grinding cup 10 is rotationallysymmetric relative to its longitudinal center axis 14.

The free end of the wear part 12 has a recess 15 in the shape of aspherical segment, when the cutting inserts 16 to be ground havesemi-spherical free ends. The cutting insert is preferably made ofcemented carbide. If the cutting insert however, has ballistic, conicalor other shape on its free end, the recess will of course have acorresponding shape. The recess 15 is adapted to be in engagement andcooperate with the free end of a cutting insert to be ground. The wearpart is made of sintered powder and at least the recess is beingprovided with an abrasive material, preferably diamond. The other partsof the grinding cup is preferably made from steel.

The intermediate portion 13 of the grinding cups 10 can be provided witha key grip at its upper portion provided to cooperate with a drivingmeans of the grinding machine to rotate the grinding cup 10. A centralflush channel 18 extending axially, extends between the free end of theshank 11 and a central and/or eccentric orifice in the recess 15. Theshank 11 and the intermediate portion 13 may alternately be providedwith other conventional geometries, suited for different kinds ofgrinding machines available on the market.

The radially outermost border line of the recess 15 has a diameter D.Radially outside the outermost border line, the wear part is providedwith a backed-off conical surface 19 or a circular surface perpendicularto the center axis 14. Said surface 19 connects to the jacket surface 20of the wear part over an obtuse 21 or perpendicular corner. The jacketsurface connects to a first part 17 of the intermediate portion 13,either continuously or via a transition such as a corner 22. The part 17has an outer diameter which may be larger than but preferably equal toor less than the diameter of the jacket surface. The first part ispreferably made integral with the wear part. The wear part 12 mayalternately be bonded to the first part 17 in another manner, preferablyby brazing. The first part 17 is firmly connected via a first joint 24to a second part 23 by gluing or vulcanization. The second part 23consists of a flexible, vibration dampening material, such as rubber forexample. The second part is furthermore connected to a third part 25 ofthe portion 13, which in turn is connected to the shank 11. The thirdpart 25 is firmly connected via a first joint 26 to the second part 23by gluing or vulcanization. The center hole of the second part has adiameter that preferably is larger than the diameter of the flushchannel 18 to avoid decrease in flow. The joint surfaces 24 and 26 arepreferably plane parallel and perpendicular to the center axis 14 of thegrinding cup. Alternately the joint surfaces may be curved. The flushchannel 18 extends centrally through the parts 17, 24 and 25. Thediameters of the latter parts are substantially equal and preferablylarger than the diameter D of the recess, said grinding cup obtaining arelatively good stability, via guiding radially close to the jacketsurface or in the jacket surface, simultaneously as transfer of thevibrations is prevented.

The described grinding cup 10 functions as follows. The grinding cup 10is mounted in the rotatable spindle of a grinding machine. The grindingcup is thereafter adjusted in position relative to the cutting insert tobe ground, i.e. in a position where the wear part 12 is in contact withthe cutting insert. The grinding cup 10 is then rotated to performgrinding of the cutting insert.

Flushing medium is supplied from an outer source to the recess 15 viathe flush channel 18. Substantially all flushing medium shall besupplied to the active surface of the cutting insert. Driving of thewear part 12 is done via the second part 23, which is flexible in boththe tangential and axial directions and the vibrations that arise willbe leveled in the part 23.

In FIG. 2 is shown an alternative embodiment of a grinding cup 10'according to the present invention. The only thing that differs from theembodiment according to FIG. 1 is that the second part 17 of theintermediate portion 13 has been expelled and thus that the second part23' has been joined directly to the wear part 12' via the joint surface24'. The third part 25' is thus a larger piece of the part 13' comparedto the embodiment according to FIG. 1. Otherwise the information givenin connection with FIG. 1 is true also for this embodiment.

In FIG. 3 is shown still another alternative embodiment of a grindingcup 10" according to the present invention. The only thing that differsfrom the embodiment according to FIG. 1 is primarily that the third part25" of the intermediate portion 13" has the shape of a socket. Thesocket has a central cylindrical cavity 27", which is provided toreceive a flexible second part 23" in its entirety and partly the firstpart 17". The second part 23" is vulcanized or glued to the socket andto the first part via joint surfaces 24" and 26". The joint surfaces arepreferably plane parallel and perpendicular to the center axis of thegrinding cup. A gap 28" is provided in the radial direction between thesecond part 23" and the cylindrical wall of the cavity 27", in order tocreate a space for expansion for the part 23", which is needed when thegrinding cup 10" is subjected to axial load. An advantage with thisalternative embodiment is that the part 17" can be guided by thecylindrical inside of the socket at angled loads on the wear part 12".

The three embodiments 10-10" described above provide the advantage thatthe grinding cup reduces transfer of vibrations from the grinding cup tothe grinding spindle in connection with grinding of drill bit cuttinginserts in combination with a simple handling and a good length of life.

In FIGS. 4 and 5 is shown still another alternative embodiment of agrinding cup 10"' according to the present invention, partly incross-section. The shank 11"' has an external thread at its free end,which in a threaded connection 29"' cooperates with an internal threadof the intermediate portion 13"' of the third part 25"'. The part 25"'has an internal cavity 27"' which consists of at least two substantiallycylindrical surfaces, an upper surface 30"' of which has a largerdiameter than a lower surface 31"'. The threaded connection provided totightened in working direction of the machine. The second part 23"'consists of a flexible means which dismountably abuts against the wearpart and the shank via contact surfaces 24"' and 26"', respectively. Aradial gap 28"' is provided between the part 23"' and the upper surface30"', in order to create a space for expansion for the part 23"', whichis needed during axial loading of the grinding cup 10"'. The wear partis partly received by the lower surface 31"' and in a central hole 32"'connected to the latter surface. A collar 33"' is provided between thehole and the lower surface. The collar cooperates with a peripheralshoulder 34"' on the wear part, facing towards the recess 15"', to forman axially forward stop. A groove 35"' is provided in the shoulder toreceive a driving pin 36"', axially secured in the part 25"'.

The described grinding cup 10"' is mounted as follows. The wear part12"' is placed in the part 25"' such that the pin enters the groove 35"'whereafter the wear part is pushed down, such that the shoulder and thecollar mutually engage. Then the means 23"' is placed in position toabutment against a rear side of the wear part, the largest diameter ofsaid means preferably being less than the smallest diameter of thethreaded portion of the part 25"'. Then the threaded connection 29"' istightened until the part 23"' has been compressed to a desired degree.An advantage with this alternative embodiment is that the wear part 12"'may be exchanged separately, such that the same shank may be used forgrinding different shapes of cutting inserts. Furthermore, the rigidityand the neutral frequency of the grinding cup can be adjusted dependingon machining conditions.

The present invention thus relates to a grinding cup where the wear partis resilient in the grinding cup in at least the axial directionrelative to the shank and where the resilient means forms contactsurfaces with connecting parts, said contact surfaces havingsubstantially the same radial extension. By that the grinding cup willachieve a good length of life by avoiding entrance of abrasive materialto the contact surfaces. The means 23-23"' preferably seals between theshank and the wear part such that the flow of flushing medium ismaintained. It is understood that the flush channel in the wear part maybe centrally or eccentrically placed.

What is claimed is:
 1. A grinding cup provided to be rotatably mountedin a grinding machine, said grinding cup being provided to performgrinding of cutting inserts of a rock drill bit, said grinding cuphaving a central axis and comprising a shank, at least one flush channeland a wear part, which includes a recess wherein the flush channelterminates, said recess performing the grinding of the cutting inserts,said grinding cup being provided with vibration dampening means, whereinthe wear part is provided resilient in the grinding cup in at least anaxial direction relative to the shank, said vibration dampening meansincluding a contact surface which is disposed against an additionalcontact surface, said contact surfaces having substantially the sameradial extension from said central axis.
 2. Grinding cup according toclaim 1, wherein the contact surfaces are substantially plane paralleland perpendicular to the center axis of the grinding cup and that thecontact surfaces are provided axially in front of the shank.
 3. Grindingcup according to claim 1, wherein the vibration dampening meanscomprises a central hole with at least substantially the same diameteras a diameter of the flush channel.
 4. Grinding cup according to claim1, wherein a space is provided in the radial direction about thevibration dampening means for the purpose of allowing radial expansionof the vibration dampening means.
 5. Grinding cup according to claim 1,wherein the contact surfaces have at least substantially the samediameter as the largest diameter of the recess.
 6. Grinding cupaccording to claim 1, wherein the vibration dampening means consists ofa hollow disc or a hollow cylindrical piece of rubber and that thevibration dampening means is glued, vulcanized or clamped against theadditional contact surface.
 7. A wear part for a grinding cup providedto be rotatably mounted in a grinding machine for grinding of cuttinginserts of a rock drill bit, said wear part being provided to be securedto a shank, a flush channel being provided to supply flushing medium tothe wear part, which has a recess, said recess performing the grindingof the cutting inserts, said wear part including a vibration dampeningmeans and having a substantially cylindrical basic shape and a centeraxis, wherein the wear part is provided with an axially rear surface,facing away from the recess, that is provided to constitute amechanically connected support surface against said vibration dampeningmeans.
 8. Wear part according to claim 7, wherein that the surface has asubstantially circular ring shape around the flush channel.
 9. Wear partaccording to claim 7, wherein that a peripheral shoulder facing towardsthe recess, is provided on the wear part and that the wear part hasdriving means.
 10. Wear part according to claim 7, wherein that thevibration dampening means is connected to an axially rear surface of thewear part.
 11. A grinding cup for a grinding machine, comprising:a shaftfor rotatable mounting in a grinding machine, said shaft including achannel and having a central axis; a wear part including a recess forthe grinding of cutting inserts, said wear part being disposed about theshaft; an intermediate portion affixed to said shaft; and vibrationdampening means disposed about said shaft, said vibration dampeningmeans being connected between said intermediate portion and said wearpart via contact surfaces, said contact surfaces having substantiallythe same radial extension from said central axis.
 12. The grinding cupof claim 11, wherein said intermediate portion and said shaft areintegrally formed.
 13. The grinding cup of claim 11, wherein saidintermediate portion and said vibration dampening means are connected byglue, vulcanization, or clamping.
 14. The grinding cup of claim 11,wherein said vibration dampening means comprises a central hole with atleast substantially the same diameter as a diameter of said conduct ofsaid shaft.
 15. The grinding cup of claim 11, wherein said vibrationdampening means is cylindrical and made from rubber.